The article by M. L. Anson describes a method for estimating the activity of pepsin, trypsin, papain, and cathepsin using hemoglobin as a substrate. The method involves digesting denatured hemoglobin with the enzyme under standard conditions, precipitating the undigested hemoglobin with trichloracetic acid, and then measuring the amount of unprecipitated protein split products using a phenol reagent that turns blue with tyrosine and tryptophan. Hemoglobin is used because it is a reproducible substrate that is not affected by peptidase. The article details the preparation of hemoglobin, the digestion and color development procedures, and the calculation of activity units. It also includes specific protocols for each enzyme, such as the activation of papain and the temperature for cathepsin digestion. The activity units are defined as the amount of enzyme that digests hemoglobin under standard conditions, and the article provides guidelines for constructing activity curves.The article by M. L. Anson describes a method for estimating the activity of pepsin, trypsin, papain, and cathepsin using hemoglobin as a substrate. The method involves digesting denatured hemoglobin with the enzyme under standard conditions, precipitating the undigested hemoglobin with trichloracetic acid, and then measuring the amount of unprecipitated protein split products using a phenol reagent that turns blue with tyrosine and tryptophan. Hemoglobin is used because it is a reproducible substrate that is not affected by peptidase. The article details the preparation of hemoglobin, the digestion and color development procedures, and the calculation of activity units. It also includes specific protocols for each enzyme, such as the activation of papain and the temperature for cathepsin digestion. The activity units are defined as the amount of enzyme that digests hemoglobin under standard conditions, and the article provides guidelines for constructing activity curves.